Method for molding aluminum and aluminum alloy powder

ABSTRACT

A powder molding method of aluminum and aluminum alloy includes: preparing a feedstock by kneading aluminum powder, aluminum alloy powder, or aluminum composite powder containing a reinforcing material with a thermoplastic organic binder; molding the feedstock to a product having a complex shape via powder injection molding, compression molding, or extrusion molding; and then producing a high-density sintered body having relative density of at least 96% by performing debinding and sintering in a single heating process under an argon gas atmosphere.

TECHNICAL FIELD

The present invention relates to a precision part manufacturing technology, whereby a product having a complex and precise shape is manufactured to a near net shape via a powder molding method, such as powder injection molding, warm compression molding, warm powder extrusion, or the like by using metal powder of aluminum or aluminum alloy as a raw material.

Further, the present invention relates to a precision part manufacturing technology, whereby a precision part is manufactured by a composite material, in which aluminum or aluminum alloy is reinforced with a ceramic or another inorganic reinforcing material.

BACKGROUND ART

Various precise shape manufacturing technologies are available as powder molding processes, such as powder injection molding, warm compression molding, warm powder extrusion, etc., whereby a complex shape is formed by using a feedstock including a powder material and a sufficient amount of an organic binder. In particular, as already well-known in the prior art, a powder molding method is widely used as a technology of economically mass-producing a complex-shaped product made of various powder materials of various metals or alloys, intermetallic compounds, ceramics, and metal-ceramic composites.

In general, relatively coarse powder is used in a conventional powder metallurgy method of processing an aluminum powder material, and about 1.5 wt % of a lubricant/surfactant is mixed with metal powder and used as a raw material so as to reduce friction that occurs during compaction. In addition, since the conventional powder metallurgy method relies on uniaxial molding, a relatively simple shape is formed, and by applying high compaction pressure to form a shape, plastic deformation of metal powder is induced so that an inter-particle contact area is increased while green density is increased and initial pore content is reduced, thereby enhancing densification during a sintering process afterward. To attain such high sintered density, relative density of a green body may be generally set to be about 90% or higher compared to theoretical density, in the conventional powder metallurgy method.

On the other hand, in powder injection molding, a feedstock, which is prepared by kneading metal powder with a large amount of about 30 to 40 vol. % of an organic binder to possess high fluidity, is used as a raw material, and thus a complex-shaped product may be manufactured. Also, a product may be molded under a low pressure far below compaction pressure of the conventional powder metallurgy method, and metal powder in a molded body during molding is subjected to pressure close to hydrostatic pressure transmitted through an organic binder, thus does not experience plastic deformation.

Since metal powder present in a powder injection molded body is in a loosely filled state, sinterability of the metal powder is very important for densification during sintering. In this regard, a powder injection molding method uses fine powder compared to powder used in the conventional powder metallurgy method.

Currently, the powder injection molding method has been applied to various metals and alloys including iron-based alloys and stainless steels, and has been accepted as a proven technology for manufacturing a product having a complex and precise shape to a near net shape. However, a powder injection molding technology has not yet been used industrially for aluminum and aluminum alloys.

The reason why the powder injection molding method is not industrially used for aluminum or aluminum alloys mainly is that it is difficult to manufacture a high-density sintered body. An oxide film having the thickness of tens to hundreds of Å is present on a surface of aluminum, owing to high affinity with oxygen.

Since the oxide film on the surface of aluminum is chemically very stable, reduction is practically impossible at a low temperature equal to or lower than the melting point of aluminum, i.e., 660° C., only by controlling oxygen partial pressure. Accordingly, due to the presence of such an oxide film that acts as an obstacle to material transfer between the adjacent particles in contact for densification, aluminum has been recognized as a material that is not suitable for the powder injection molding method.

In general, one of methods for removing an oxide film formed on a surface of aluminum powder is adding, to the aluminum powder, an element having higher affinity with oxygen than aluminum, such as magnesium powder. The added magnesium powder reacts chemically with the oxide film during sintering to form magnesium spinel, accompanying local reduction of aluminum, via a chemical reaction of 4Al₂O₃+3Mg=3MgAl₂O₄+2Al. Such a method is very effective, and in effect, almost all commercialized powder metallurgy aluminum alloys contain at least 0.5 wt % of magnesium, such as Al—Cu—Mg (Ecka Alumix® 13 and Ecka Alumix® 123 of Ecka Granules Inc., Germany; and Ampal 2712, Ampal 2905 of Ampal Inc., U.S.A) (Alumix® is a registered trademark of Ecka Granules Inc.) (corresponding to wrought AA2024 of American Aluminum Association), Al—Mg—Si—Cu (Ecka Alumix® 321 of Ecka Granules Inc., Germany; and AMPAL 6711 of Ampal Inc., U.S.A) (corresponding to wrought AA6061); and Al—Zn—Mg—(Cu) (Ecka Alumix® 431 of Ecka Granules, Germany; and AMPAL 7775 of Ampal Inc., U.S.A) (corresponding to wrought AA7075).

While sintering a green compact of aluminum and aluminum alloy powder via a conventional powder metallurgy method, various atmospheres, such as nitrogen, argon, hydrogen, and vacuum, may be used, and among others, a nitrogen gas is known to produce the highest sintered density. In fact, the nitrogen gas is widely used as a sintering atmosphere gas in general aluminum powder metallurgy industries. Although it has been acknowledged that a nitridation reaction of Al+(1/2)N₂=AlN may spontaneously occur between aluminum powder and nitrogen gas, the aforesaid nitridation reaction takes place scarcely or limitedly in a green compact having a high relative density of 90% or higher, produced by the conventional powder metallurgy method, and thus the nitridation reaction has not been considered to be problematic.

However, the nitridation reaction may cause a big problem when a nitrogen gas is used as an atmospheric gas during a sintering process of a powder molded body according to the present invention, which is made of fine metal powder having a large specific surface area and a high reactivity, and having porosity of 50% to 10% after debinding. That is, since the surface of aluminum powder is exposed to the nitrogen gas even before the onset of a sintering reaction between particles during debinding and further heating for a sintering, an aluminum nitride starts to form, and thus atomic migration across the interface between adjacent aluminum powders being in contact is inhibited, inter-particle bonding and densification during the sintering process are interfered.

Another reason why powder injection molding of aluminum is difficult compared to other metals is that a melting point of aluminum or a solidus temperature at which an aluminum alloy is liquefied and starts to melt is remarkably low compared to other metals, such as iron, stainless steel, nickel, copper, cobalt, titanium, etc., or alloys thereof. Accordingly, an organic binder used for powder injection molding of aluminum may be removed at a lower temperature.

Another problem to be solved during debinding and sintering of an aluminum molded body containing a large amount of an organic binder is formation of aluminum carbide (Al₄C₃) through a reaction between decomposed product of the organic binder and aluminum. The aluminum carbide is brittle and is undesirable since it reacts with moisture by a reaction of Al₄C₃+6H₂O=2Al₂O₃+3CH₄. In this regard, it is necessary to use a proper organic binder composition and accurately control the debinding process.

Hereinafter, prior arts relevant to powder injection molding of the aluminum and aluminum alloys reported so far will be briefly reviewed.

In U.S. Pat. No. 5,525,292, Nakao et al. describe a process of producing a part made of aluminum alloy powder mixed with magnesium as an alloying element and compression-molded in a nitrogen gas atmosphere such that relative density becomes 60 to 85%. After removing a lubricant by adding magnesium up to about 2% and then additionally charging a magnesium lump inside a furnace to perform sintering, the pressure inside the furnace is reduced to induce sublimation of magnesium, a nitrogen gas is then introduced and heated to a high temperature to perform sintering. Nakao et al. claimed that sublimated magnesium vapor reacts with a nitrogen gas to form Mg₃N₂, which in turn reacts with an aluminum oxide on a surface of aluminum powder to result in reduction of an aluminum oxide film into aluminum metal locally, thereby enhances the sinterability of aluminum powder.

WO 2005/066380 discloses that in order to enhance sintered density of aluminum powder and aluminum alloy powder packed loosely without applying external pressure, sintering in a nitrogen gas atmosphere is effective in which partial pressure of water vapor is in the range of about 0.003 kPa to 0.015 kPa.

In U.S. Pat. No. 6,761,852, Yeo and Tian proposed, in order to remove an oxide film on a surface of aluminum powder, a method of removing an aluminum surface oxide film by using a low temperature eutectic reaction between metal salts being selected from NaF, MgF₂ and CaF₂ and alumina. After an injection molded body is debound in solvent, the injection molded body is subjected to thermal debinding and sintering. As the aluminum oxide film is removed through a reaction with metal salts to form low temperature eutectic liquid and densification proceeds to form a high-density sinter with a relative density of 95% or higher, and it is claimed that sintering in vacuum is advantageous.

In WO 2008/017111, Liu et al. disclosed that by using tin having a low melting point as a sintering aid, a nitrogen gas as an atmospheric gas, and a magnesium lump as an oxygen getter being placed in a furnace to perform sintering, a high-density sinter may be produced; addition of 2 wt % of tin powder to AA6061 aluminum alloy powder and placing a magnesium lump as oxygen getter. It was claimed that after sintering at 620° C. for 2 hours, relative density of about 97%, tensile strength of 165 MPa, and elongation of about 9% were obtained, and further, after T6 artificial aging, tensile strength of 300 MPa and elongation of 1% were obtained.

In “Sintering Parameters and Mechanical Properties of Injection Moulded Aluminium Powder,” Powder Metallurgy, vol. 54 (no. 2) (2011) pp. 427-431, L. Acar and H. O. Gulsoy claimed that, using a feedstock with a solids loading of 62.5%, including of aluminum powder (manufactured by Ecka Granules Co., Ltd) having an average size of 7.35 μm, a molded body was produced by injection molding, which is then subjected to two-stage debinding of solvent extraction in heptane followed by thermal debinding in a nitrogen gas, and finally sintered at 650° C. to produce a sinter having a relative density of 96.2%.

In WO 2010/020066 and the article published in 2012 (C. Giert et al., “Carbon Removal as a Crucial Parameter in the Powder Injection Moulding of Aluminum Alloys,” Powder Injection Moulding International, vol. 6 (No. 4) (2012) pp. 65-71), Giert et al described aluminum powder injection molding using a feedstock including aluminum (Al) and aluminum-magnesium (Al—Mg) powder and Catamold™ (Trademark of BASF, Germany) organic binder which is known as an organic binder consisting of wax and polyacetal. It has been proposed that high-density sinter is obtained by catalytic debinding using a vapor of nitric acid or oxalic acid as a catalyst, followed by thermal debinding of remaining organic binder constituent in a nitrogen gas containing at least 0.5 vol. % of oxygen and sintering in the nitrogen gas.

As described above, various methods have been proposed for powder injection molding of aluminum and alloy thereof, but a method of precisely producing a complex-shaped product while properly realizing mechanical properties of aluminum alloys has not been provided yet.

DESCRIPTION OF EMBODIMENTS Technical Problem

Provided is a powder injection molding method capable of precisely manufacturing a precision part having a complex shape made of aluminum or an alloy thereof with a sintered body having relative density of 96% or higher.

Provided is a debinding process and a sintering process capable of achieving densification of high density without having to add a sintering aid having a low melting point, such as tin suggested in the prior art, with respect to manufacturing of a sintered body having high density made of aluminum or an alloy thereof via a powder injection molding method.

Provided is a debinding process and a sintering process adequate to obtain a sound and dense sintered body from a green body made of aluminum or aluminum alloy composite powder obtained by adding a reinforcing material to aluminum or an aluminum alloy.

Provided is a method of manufacturing a high-density aluminum or aluminum alloy sintered body and a precise product of an aluminum composite body applying a feedstock for injection molding to low pressure warm compression molding and extrusion molding.

The technical problems to be solved in the present invention are not confined to those mentioned above, and other technical problems may be obviously understood by one of ordinary skill in the art from descriptions below.

Solution to Problem

According to an aspect of the present invention, a powder molding method includes: preparing a feedstock by kneading aluminum powder or aluminum alloy powder with a wax-based thermoplastic organic binder containing polyolefin copolymer having a carbonyl group; molding the feedstock to obtain a molded body; debinding the wax-based thermoplastic organic binder from the molded body to obtain a debound body; and sintering the debound body under an argon gas atmosphere for densification.

In particular, the debinding and the sintering may be performed in a single process in a same furnace under an argon gas atmosphere to remove the wax-based thermoplastic organic binder from the molded body and sinter the debound body.

The aluminum powder or aluminum alloy powder may further contain at least one reinforcing material selected from the group consisting of carbide selected from SiC, B₄C, TiC and WC, nitride selected from Si₃N₄, AlN, TiN, c-BN and h-BN, oxide selected from Al₂O₃, SiO₂, Y₂O₃, fly ash, and ZrO₂, sulfide including MoS₂, boride including TiB₂, hard cobalt alloy including T-800, powder, short fiber, or whisker of a refractory metal selected from W and Mo, polycarbon, graphite, carbon nanotube, graphene, and diamond such that aluminum-matrix composite material is used.

According to another aspect of the present invention, a sintered body part is produced by using aluminum powder, aluminum alloy powder, or aluminum-matrix composite material manufactured via the powder molding method above, wherein the sintered body part is a precise-shaped product selected from an impeller, a turbine, or a linear motion bearing end cap.

Advantageous Effects of Invention

According to the present invention, a powder injection molding technology is provided, the powder injection molding technology being applicable to aluminum and aluminum alloys having many advantages as an industrial material, such as low density, high thermal conductivity and electrical conductivity, good corrosion and weathering resistance, and natural color, and in addition, having excellent mechanical properties owing to a high precipitation hardening effect depending on alloying.

In other words, according to a powder molding method of the present invention, a method of manufacturing a molded body having a complex shape from aluminum or aluminum alloy powder, and manufacturing a high-density sintered body having relative density of 96% or higher through following debinding and sintering processes is provided.

In addition, since debinding and sintering processes according to the present invention are performed in a single step in a same furnace using a single heating schedule, a separate additional facility, such as a solvent extraction system or a supercritical fluid extraction system for debinding is not required, the number of processes is reduced and accompanying energy consumption is reduced, and labor costs are reduced, and accordingly, overall production costs are reduced for economic effect.

Since aluminum or an aluminum alloy manufactured according to a powder molding method of the present invention does not necessarily include a sintering aid alloying element having a low melting point, such as tin having low solubility in aluminum, a sintered body having enhanced mechanical properties may be produced.

As such, a powder molding method according to the present invention is applicable not only to pure aluminum, but also to almost all commercial aluminum alloys including precipitation-hardenable aluminum alloys, such as Al—Cu—Mg—(Mn) series (AA 2xxx series), Al—Mg—Si series (AA6xxx series), and Al—Zn—Mg—(Cu) series (AA7xxx-series) alloys, and thus the powder molding method according to the present invention may have a significant industrial effect in production of precision parts required for various purposes.

In addition, an aluminum-matrix composite part may be manufactured by reinforcing an aluminum or aluminum alloy base with one or more materials selected from a group consisting of carbides such as SiC, B₄C, TiC and WC, nitrides such as Si₃N₄, AlN, TiN, c-BN and h-BN, oxides such as Al₂O₃, SiO₂, Y₂O₃, fly ash, and ZrO₂, sulfides including MoS₂, borides including TiB₂, hard cobalt alloys including T-800, powder, powder, short fiber, or whisker of a refractory metals such as W and Mo, polycarbon, graphite, carbon nanotube, graphene and diamond.

In particular, a powder molding method according to the present invention may be applied not only to powder injection molding, but also to warm compression molding and warm powder extrusion.

As such, as a novel technology in manufacturing a precise shape product of aluminum, aluminum alloy, and aluminum-matrix composite material, the present invention has a ripple effect of providing new manufacturing technology having high technical, economical, and eco-friendly values.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow diagram of the present invention.

FIG. 2 shows a photograph of an injection molded body of an AA6061 alloy tensile test specimen manufactured via a powder injection molding method according to the present invention before and after sintering, wherein (a) shows the injection molded body, (b) shows the injection molded body after sintering at 580° C. for 0 hours, (c) shows the injection molded body after sintering at 590° C. for 0 hours, and (d) shows the injection molded body after sintering at 610° C. for 2 hours.

FIG. 3 is a graph showing density according to a sintering time when injection molded bodies of AA6061 alloy powder (indicated by curve 1) and mixed powder (indicated by curve 2) are sintered at 610° C.

FIG. 4 shows an optical microscope microstructure of an AA6061 alloy injection specimen sintered at 610° C.

FIG. 5 shows each of tensile curves at room temperature with respect to a test specimen obtained by sintering injection molded bodies of AA6061 alloy powder and mixed powder at 610° C. for 3 hours, and a test specimen subjected to solution treatment at 540° C. for 1 hour and artificial aging treatment (T6) at 170° C. for 8 hours.

FIG. 6 is a scanning electron microscope image of a broken surface of an AA6061 alloy powder tensile test specimen that is manufactured via powder injection molding and subjected to T6 heat-treatment.

FIG. 7 is a perspective view of (a) injection molded body and (b) sintered body of an impeller fabricated using a composite powder feedstock, in which Al-1 wt % Mg-0.5 wt % Si-0.25 wt % Cu alloy powder is admixed with 1 wt % of tin powder and 5 wt % of silicon carbide powder.

FIG. 8 shows a turbine sintered body made of aluminum-silicon carbide 5 wt % composite powder, according to the present invention.

FIG. 9 is a perspective view of (a) injection molded body and (b) sintered body of a miniature linear motion bearing end cap made of AA6061 alloy powder according to the present invention, and FIG. 9 (c) is a product drawing illustrating that a dummy bar is temporarily added to the injection molded body to prevent distortion during a sintering process.

BEST MODE

An important aspect of the present invention is to overcome low sinterability of aluminum powder caused by presence of an oxide film on a surface of the aluminum powder with respect to precisely manufacturing a high-density sintered body via powder injection molding of a complex-shaped part made of aluminum or an alloy thereof.

As described above, since an aluminum oxide film formed on the surface is thermodynamically stable, reduction is almost impossible at a low temperature, such as at a sintering temperature of aluminum. Further, since aluminum powder is not subjected to plastic deformation during a powder injection molding process and exists in an organic binder in a loosely filled state, physical breakage of the aluminum oxide film on the surface of the aluminum powder is not considered.

Nevertheless, sintering occurs in a loosely packed aluminum compact because a thermal expansion coefficient of aluminum oxide is only about ⅓ of that of aluminum. In other words, due to high thermal expansion of aluminum during a heating process, an outer surface of the aluminum oxide film of the aluminum powder is broken and fresh aluminum metal is exposed, the fresh aluminum metal acting as a path for material transport between powders being in contact, thereby causing densification of powder compact. Such an effect is more effective when the sintering temperature is higher.

Of course, it is very important to keep low oxygen content in raw aluminum powder, and in this aspect, it is advantageous to use gas-atomized aluminum powder with low oxygen content to manufacture a high-density sintered body over aluminum powder produced by air-atomization.

Also, as described above, addition of an alloying element which may react with an aluminum oxide film on aluminum powder during the heating process to result in partial reduction may be considered to be effective in improving sinterability of the aluminum alloy.

As such, it is important to reduce oxygen concentration or moisture content in an atmosphere gas being used in order to fully utilize the fresh aluminum metal, which is a passage of material movement provided by physical destruction or partial reduction by a chemical reaction of the aluminum oxide film generated on the surface of the aluminum powder.

According to another aspect of the present invention, the sintering temperature of aluminum and aluminum alloys needs to be lower than the melting point of pure aluminum, i.e., 660° C., and since a solidus temperature of most commercial aluminums, where a liquid phase starts to form, is lower than or equal to 600° C., a temperature where a debinding process is completed and a temperature where a sintering process starts may overlap. Thus, it is important to avoid an undesired reaction between aluminum and a decomposed product of the organic binder occurring due to excessive liquid phase aluminum, while the debinding process is incomplete.

As described above, in order to produce a high-density sintered body, it is important to keep oxygen content in a sintering gas atmosphere as low as possible during a sintering process. In this regard, together with the use of a dry atmosphere gas containing low oxygen content, it is also effective to introduce a magnesium lump into a furnace as an oxygen getter.

However, in the present invention, a new method of promoting sintering by using an organic binder in a molded body, the organic binder having been regarded simply as a substance to be removed after injection molding, is attempted as a method of producing a high-density sintered body, without having to use a separate sintering aid or an oxygen getter.

Also, according to the present invention, a debinding process and a sintering process are performed under an argon gas atmosphere. Accordingly, addition of a sintering aid element of a low melting point, such as tin, is not essential, which was added in the prior art using a nitrogen gas sintering atmosphere to prevent formation of a nitride on a surface of aluminum powder, which inhibits densification. However, when necessary, tin may be added in an amount up to 3 wt %, but even in this case, the debinding and sintering processes may be performed under an argon gas atmosphere.

Also, according to the present invention, a debinding process and a sintering process for removing an organic binder from a molded body made of aluminum composite powder, in which aluminum or aluminum alloy powder is admixed with a reinforcing material, are the same as those of aluminum or aluminum alloy. However, since an undesirable compound may be formed due to a reaction between the aluminum and the reinforcing material during the sintering process, the composition of an alloy base may be suitably adjusted depending on the reinforcing material.

Hereinafter, the present invention will be described in detail with reference to FIG. 1.

According to FIG. 1, a powder molding method of the present invention may include: preparing a feedstock in operation S10 by kneading aluminum powder or aluminum alloy powder with a wax-based thermoplastic organic binder containing polyolefin copolymer having a carbonyl group; molding the feedstock to obtain a molded body in operation S20; debinding the wax-based thermoplastic organic binder in operation S30 from the molded body to obtain a debound body; and sintering the debound body in operation S40 under an argon gas atmosphere for densification.

In particular, according to the present invention, to enhance sinterability of the aluminum powder or the aluminum alloy powder, sinterability may be secured by selecting aluminum or aluminum alloy powder whose size is finer than that used in conventional powder metallurgy and oxygen content is not high.

Accordingly, an average particle size of the aluminum or aluminum alloy powder may be in the range of 0.5 to 20 μm, and for example, in the range of 1 to 15 μm.

According to the present invention, the aluminum alloy powder may be a prealloyed powder produced by atomization of alloy in molten state, or blended powder in which pure aluminum and another alloying element powder or master alloy powder, such as Al—Mg, for addition of another alloying element are mixed.

According to the present invention, it is not essential to use, as a sintering aid, an element having a low melting point, such as tin, from among alloying elements, for enhancing high-density sintering.

However, the sintering aid, specifically tin or tin oxide (SnO), may be added in such a small amount when necessary, wherein tin may be added 0.1 to 3 wt % and tin oxide may be added 0.3 to 5 wt % based on 100 wt % of the aluminum powder or the aluminum alloy powder. However, such a sintering aid may improve sintered density, but may adversely affect mechanical properties. Also, in the present invention, even when the sintering aid is added, the present invention may be implemented under an argon gas atmosphere rather than a nitrogen gas atmosphere.

According to the present invention, the organic binder used in operation S10 may be a wax-based thermoplastic organic binder or a well-known composition having a composition ratio similar to the wax-based thermoplastic organic binder, wherein the wax-based thermoplastic organic binder contains wax as a basic component, polyolefin, polyolefin copolymer, or a combination thereof as a back-bone polymer, another organic compound acting as a surfactant or a lubricant, and has a debinding temperature of 490° C. to 540° C.

Examples of the wax-based thermoplastic organic binder that may be effectively used in the present invention include paraffin wax, microcrystalline wax, a polyolefin copolymer having a carbonyl group, polyolefin wax, and other organic binder compositions including additives added as needed.

In particular, the wax-based thermoplastic organic binder may be an organic binder composition including a polyolefin copolymer having a carbonyl group 3 to 30 wt % based on 100 wt % of organic binder composition.

According to the present invention, operation S20 may be performed via a method selected from powder injection molding, warm compression molding, and warm powder extrusion.

According to the present invention, the debinding of operation S30 may be thermal debinding using a neutral gas as a carrier gas.

Alternatively, the thermal debinding combined with solvent extraction in hexane or heptane or supercritical fluid extraction using carbon dioxide may also be used. In this case, two-step processes are performed, wherein partial debinding is performed by the solvent extraction or the supercritical fluid extraction to remove a low melting point organic compound such as wax, surfactant, or the like, and then thermal debinding is performed to remove the remaining organic binder components, such as back-bone polymer, etc.

A carrier gas used in the thermal debinding of the present invention may be an argon gas.

Also, according to the present invention, the sintering process for densifying the debound body to the sintered body having relative density of at least 96% may be performed under an argon gas atmosphere, performed in vacuum (10⁻³ torr or below), or performed in partial vacuum with circulation of an argon gas as a sweep gas while maintaining a vacuum state level of about 10 to 200 torr. However, particularly for a debound aluminum alloy body, an argon gas at the ambient pressure may be used as a sintering atmosphere gas.

An argon gas used in operations S30 and S40 may be a dry gas having low moisture content, a flow rate of 0.1 to 20 L/min, and a dew point of −40° C. or less.

In particular, according to the present invention, when only thermal debinding is employed in operation S30, both the debinding and the sintering may be performed as a single heating step. When both the debinding and the sintering are performed in a same furnace using a single heating schedule, a higher densification effect may be attained and a high-density sintered body may be easily obtained.

According to the present invention, for commercially pure aluminum powder which contains 0.5 wt % or less of an alloying element, sintering may be performed at a temperature in the range of 630° C. and 655° C.

According to the present invention, in order to obtain a defect-free and high-density aluminum alloy sintered body using the aluminum alloy powder, a solidus temperature of the aluminum alloy powder may be equal to or higher than 480° C., preferably, equal to or higher than 520° C., and more preferably, equal to or higher than 540° C.

For the molded body made of the aluminum alloy powder, wherein total content of alloying elements added to the aluminum alloy powder is 0.5 to 12 wt % based on 100 wt % of the aluminum alloy powder, a sintering temperature may be ranging from a solidus temperature to a temperature where an amount of a liquid phase becomes 30 vol. % based on 100 vol. %.

Further, according to the present invention, an aluminum alloy in the aluminum alloy powder may be a commercial aluminum alloy composition containing at least 0.5 wt % of magnesium and selected from the group consisting of Al—Cu—Mg—(Mn) series (AA2xxx), Al—Mg series (AA5xxx), Al—Mg—Si—(Cu) series (AA6xxx), Al—Zn—Mg—(Cu) series (AA7xxx), or a composition containing 0.5 to 8 wt % of magnesium, 0 to 8 wt % of zinc, 0.1 to 3 wt % of copper, 0 to 5 wt % of silicon, 0 to 5 wt % of nickel, 0 to 0.3 wt % of iron, 0 to 1 wt % of manganese, 0 to 0.5 wt % of zirconium, 0 to 0.5 wt % of chromium, 0 to 2 wt % of silver, 0 to 0.5 wt % of scandium, 0 to 2 wt % of lithium, and the balance of aluminum in total 100 wt %.

Further, instead of using the aluminum alloy powder, blended powder mixture of a pure element such as aluminum, magnesium, copper, silicon, zinc, or a master alloy containing thereof may be used.

The sintering in the present invention may be performed under an argon gas atmosphere or in vacuum, in particular, may be performed under an argon gas atmosphere.

In case of pure aluminum, the sintering may be performed under an argon gas atmosphere first, and then in vacuum for at least 1 hour to improve sintered density.

In addition, the present invention provides the powder molding method using an aluminum-matrix composite material obtained by adding, to the aluminum powder or the aluminum alloy powder, one or more reinforcing materials selected from a group of carbide comprising SiC, B₄C, TiC and WC, nitride comprising Si₃N₄, AlN, TiN, c-BN and h-BN, oxide comprising Al₂O₃, SiO₂, fly ash, Y₂O₃, and ZrO₂, sulfide such as MoS₂, boride including TiB₂, hard cobalt alloy such as T-800, powder, short fiber, or whisker of a refractory metal such as W or Mo, polycarbon, graphite, carbon nanotube, graphene and diamond.

An average diameter of the reinforcing material may be 0.05 to 40 μm, and the reinforcing material may be added in the amount ranging from 1 to 30 wt % to 100 wt % of the aluminum powder or the aluminum alloy powder.

The present invention provides a sintered body part of the aluminum powder, the aluminum alloy powder, or the aluminum-matrix composite material manufactured by the powder molding method. An example of the sintered body part includes a precise shaped product selected from an impeller, a turbine, and a linear motion bearing end cap, but is not limited thereto.

MODE OF INVENTION

Hereinafter, a method of producing a high-density complex-shaped product having relative density of at least 96% by using aluminum or aluminum alloy powder via powder injection molding, according to the present invention, will be described in detail through following examples. However, the present invention is not limited to these examples.

Example 1

A 300 g of feedstock having a solids loading of 62% was prepared by kneading aluminum powder having purity of 99.5% and an average particle size of about 6 μm (MEP 105, Ecka Granules, Germany) and an organic binder containing 70 wt % of paraffin wax, 16 wt % microcrystalline wax, 6 wt % maleic anhydride grafted polyethylene (DP-730, Hyundai EP, Korea) as a polyethylene copolymer having a carbonyl group, and 8 wt % polyethylene wax in a pressurized kneader at 140° C. for 2 hours. The resulting feedstock was crushed into about 6 mm sized granules, charged into an injection molding machine having clamping force of 80 tons, and injection-molded to produce an injection molded body of a tensile test specimen of ASTM subsize standard (ASTM E8).

The injection molded body was cut and inspected visually to examine presence of an internal defect and also through an X-ray non-destructive test, and it was confirmed that the injection molded body was defect-free.

After placing the injection molded body of the tensile test specimen in an alumina boat and charging it into a tube furnace, debinding-sintering was performed in the same tube furnace in a single heating schedule while flowing an argon gas (a dew point of −54° C.) at a rate of 0.3 L/min.

In the debinding-sintering, a temperature was initially increased from room temperature to about 100° C. in 1 hour and held for 1 hour; increased to 280° C. in 4 hours and held for 3 hours; increased to 380° C. in 4 hours and held for 3 hours; increased to 520° C. in 2 hours and held for 30 minutes; increased to 650° C. in 1.5 hours and held for 2 hours; and then decreased to room temperature. A sintered body of the tensile test specimen manufactured as such had no apparent defect and exhibited a silver white color. The sintered body showed a linear shrinkage of about 12.8%. Relative density was 96% based on a result of density measurement using the Archimedes principle. In a phase analysis by an X-ray diffraction experiment, formation of aluminum carbide (Al₄C₃), which is known as a harmful compound, was not detected. A room-temperature tensile test revealed 0.2% yield strength of 71 MPa, tensile strength of 132 MPa, and elongation of about 20%.

Comparative Example 1

An injection molded body of a tensile test specimen as manufactured in Example 1 was used as a specimen, and an evaluation experiment was performed to investigate an effect of a type of gas on sintering by changing a gas atmosphere to a nitrogen gas atmosphere. The specimen was charged into a tube furnace, and debinding and sintering were performed using a single heating schedule as used in Example 1. The only difference was the use of 99.99% of a pure nitrogen gas instead of an argon gas, which was flowed at a rate of 0.3 L/min. A sintered specimen manufactured as such exhibited dark-brown color, showed almost no shrinkage, and showed some brittleness. The sintered specimen was porous and relative sintered density was about 63%. Based on a result of a phase analysis by an X-ray diffraction experiment, the sintered body contained about 20 wt % of AlN.

Example 2

About 50 g of feedstock having a solids loading of 65% was prepared at 135° C. for 2 hours by kneading, in a twin-cam mixer (Rheocord 90, Haake, Germany), gas-atomized 99.8% purity aluminum powder (Aluminum powder company, U.K.) having an average particle size of about 6 pm and an organic binder containing 60 wt % paraffin wax, 26 wt % microcrystalline wax, 8 wt % maleic anhydride grafted polyethylene (DP-730, Hyundai EP, Korea) as the polyolefin copolymer having a carbonyl group, and 6 wt % polyethylene wax.

The feedstock was crushed into about 3 mm granules by using a steel mortar and pestle, charged into a steel mold preheated to 120° C., and then compression-molded under pressure of 20 MPa to manufacture an molded body of a small and non-standard tensile test specimen having a total length of 50 mm, a length of a parallel section of 20 mm, a width of a grip section of 16 mm, and a width of the parallel section of 5 mm.

After placing the molded body of the tensile test specimen manufactured as such in an alumina boat and charging it into a tube furnace, debinding-sintering was performed in a same furnace at a sintering temperature of 650° C. for a sintering time of 2 hours in a single heating schedule like Example 1, while flowing an argon gas (a dew point of −54° C.) at a rate of 0.3 L/min. A sintered body of the tensile test specimen manufactured as such exhibited a bright silver white color and revealed shrinkage of about 12.8%. The density measurement by the method based on the Archimedes principle showed a relative density of 97.8%. In the phase analysis by the X-ray diffraction experiment the formation of Al₄C₃ phase was not detected. Relative density was 97.8% based on a result of density measurement using the Archimedes principle.

Example 3

A 500 g of feedstock having a solids loading of 67% was prepared by kneading gas-atomized AA6061 aluminum alloy powder (Al-0.91 wt % Mg-0.70 wt % Si-0.26 wt % Cu, Aluminum powder company, U.K.) having an average particle size of about 6 μm with an organic binder containing 58 wt % paraffin wax, 26 wt % microcrystalline wax, 10 wt % maleic anhydride grafted polyethylene (DP 730, Hyundai EP, Korea) as a polyolefin copolymer containing a carbonyl group, and 6 wt % polyethylene wax, in a double-blade planetary mixer at 140° C. for 2 hours. The resulting feedstock was crushed into granules, charged into a hopper of an injection molding machine, and injection-molded to form a defect-free injection molded body of a tensile test specimen without any internal defect. In addition, another specimen having a disc shape with a diameter of 20 mm and a height of 4 mm was prepared via warm compression molding using a steel mold preheated to 118° C.

The tensile test specimen was placed on an alumina tray and charged into a tube furnace. Debinding and sintering were performed in a single heating schedule while flowing an argon gas (a dew point of −53° C.) at a rate of 0.3 L/min. A temperature was initially increased from room temperature to about 100° C. in 1 hour and held for 1 hour; increased to 280° C. in 2 hours and held for 3 hours; increased to 380° C. in 4 hours and held for 3 hours; increased to 520° C. in 2 hours and held for 30 minutes; and then increased to a sintering temperature at a rate of about 1.5° C. per minute. Here, the sintering temperature was changed between 580 to 630° C. and a sintering time was changed between 0 to 4 hours to repeatedly perform a debinding-sintering experiment, thereby determining the optimum sintering condition.

FIG. 2 (a) shows an injection molded body, (b) shows a sintered body at 580° C. for 0 hours, (c) shows a sintered body at 590° C. for 0 hours, and (d) shows a sintered body at 610° C. for 2 hours, wherein the sintered bodies exhibited a silvery white color. Formation of Al₄C₃ was not detected in an X-ray diffraction experiment performed on the sintered body. Density of the sintered body was determined via a density measuring method using the Archimedes principle and converted to relative density. Change of sintered density was examined while changing a sintering temperature based on a sintering time of 3 hours, and relative density was found to be 94% at 580° C. and about 98% at a temperature in the range of 600° C. and 630° C. with no appreciable difference. Under such a sintering condition, linear shrinkage was about 12%. As a result, the optimum sintering temperature was determined to be in the range of about 600° C. and 630° C.

Further, a result of examining density according to a sintering time at 610° C. is shown in FIG. 3 (curve 1). Relative density was already 94% when a sintering temperature was just reached, and after 1 hour of sintering, the relative density was increased to 98%. FIG. 4 shows a microstructure of a specimen sintered at 610° C. and observed under an optical microscope after polishing. The microstructure appeared homogeneous and defect-free without large pores. FIG. 5 shows tensile curves obtained by performing tensile tests at room temperature with respect to a sintered body specimen sintered at 610° C. for 3 hours and a specimen subjected to solution treatment at 540° C. for 1 hour and artificial aging treatment (T6) at 170° C. for 8 hours. Based on results of the tensile tests, the sintered body specimen showed 0.2% yield strength of 91 MPa, tensile strength of 221 MPa, and elongation of 20.7%, the specimen on which T6 was performed showed 0.2% yield strength of 302 MPa, tensile strength of 336 MPa, and elongation of 6.3%. FIG. 6 shows an image of a fracture surface of the specimen after the tensile test, observed in a scanning electron microscope, wherein a dimple structure that is a typical image appearing on a fracture surface of a ductile material is revealed.

Comparative Example 2

A molded body prepared in the same manner as Example 3 was repeatedly tested by using a different type of atmosphere gas for debinding and sintering. In other words, a nitrogen gas of 99.99% purity was used, and was flowed at a rate of 0.4 L/min during a debinding-sintering process.

A sintered body of a tensile test specimen manufactured as such had relative density of about 62%, was porous, and was found to be brittle, and thus a tensile test was unable be performed. A phase analysis by X-ray diffraction showed that the tensile test specimen contained about 18 wt % of AlN.

Example 4

Example 4 is performed in the same manner as Example 3, by using a different type of metal powder. In other words, 250 g of blended powder having a composition of Alumix® 321 (Alumix®, a registered trademark of Ecka Granules, Germany; Al-1 wt % Mg-0.5 wt % Si-0.25 wt % Cu) similar to that of AA6061 alloy was prepared by ball milling, for 2 hours, air-atomized pure aluminum powder having an average particle size of about 5 μm (MEP 105, Ecka Granules, Germany), 99.8% pure magnesium powder having -325 mesh size (Nana AMT, Korea), 99.% pure copper powder having a particle size of 1 to 5 μm (CU-101, Atlantic Equipment Engineers, Inc., U.S.A), and 99.9% pure silicon powder having a particle size of −10 μm (SI-102, Atlantic Equipment Engineers, Inc., U.S.A).

An injection molded body of a tensile test specimen of ASTM subsize and a compression-molded test specimen were prepared by the same manner as Example 3, and were debound and sintered in a single heating schedule in the same manner as Example 3, while flowing an argon gas at a rate of 0.3 L/min. However, a sintering temperature was set to 610° C. and a sintering time was varied from 0 to 4 hours.

A curve 2 in FIG. 3 of the present experiment shows density obtained according to a sintering time. In this experiment, wherein mixed powder including elemental metal powder was used, relative density of about 96.2% was obtained after sintering for 3 hours.

Example 5

A 500 g feedstock having a solids loading of 67% was prepared in the same manner as Example 2, by kneading powder mixture containing AA6061 aluminum alloy powder (Aluminum powder company, U.K.) having an average particle size of 6 pm as in Example 2 and 1 wt % of tin (SN-101, Atlantic Equipment Engineers, Inc., U.S.A) having 99.9% purity and a particle size from 1 to 5 μm with the organic binder as used in Example 2. The prepared feedstock was granulated, and was injection-molded to produce a tensile test specimen of ASTM subsize, and a disc-shaped specimen having a diameter of 20 mm and a height of 4 mm was also manufactured via warm compression molding.

The test specimen was placed in an alumina tray and charged into a tube furnace, and then debinding and sintering were performed in a single heating schedule while flowing an argon gas (a dew point of −53° C.) at a rate of 0.4 L/min. Here, in order to determine the optimum sintering condition, the sintering experiment was repeated while changing a sintering temperature and sintering time from 580° C. to 630° C. and 0 to 4 hours, respectively.

Relative density of a manufactured sintered body of the tensile test specimen to theoretical density was calculated according to a density measuring method using the Archimedes principle. Given a sintering time of 3 hours, change of sintered density according to sintering temperature was investigated, and it was found that the relative density was 94% at 580° C., and was about 98% in a temperature range from 600° C. to 630° C. with no appreciable difference. A tensile test was performed on such a specimen, and based on a result of the tensile test at room temperature in a sintered condition, tensile strength was 215 MPa and elongation was 15.2%. The sintered body of the tensile specimen was further solution-treated at 540° C., water-quenched and artificially aged at 170° C. for 8 hours (T6) and for this specimen, tensile strength of 278 MPa and elongation of about 2.5% were obtained.

Comparative Example 3

A feedstock having a solids loading of 67% was prepared by using mixed powder containing AA6061 aluminum alloy powder (Aluminum powder company, U.K.) having an average particle size of about 6 μm as in Example 3 and 1 wt % tin (SN-101, Atlantic Equipment Engineers, Inc., U.S.A) having 99.9% purity and a particle size of 1 to 5 μm, and an injection molded body of a tensile test specimen was produced.

The produced test specimen was placed in an alumina tray and charged into a tube furnace, and then debinding and sintering were performed in a single heating schedule as used in Example 4. A sintering temperature and a sintering time were set to be 610° C. and 3 hours, respectively, as in Example 3 and 99.99% nitrogen gas was flowed at a rate of 0.4 L/min.

Sintered density of the sintered body of the tensile test specimen was determined to be about 96% based on a result of a density measuring method using the Archimedes principles. In a sintered condition, tensile strength was 214 MPa and elongation was 12%. After artificial aging (T6) at 170° C. for 8 hours following solution treatment at 540° C., the sintered body of the tensile test specimen showed tensile strength of 271 MPa and elongation of about 0.5%.

Example 6

A 500 g of feedstock having a solids loading of 67% was produced by kneading mixed powder containing AA6061 aluminum alloy powder (Aluminum powder company, U.K.) having an average particle size of about 6 μm as used in Example 3, and 1 wt % tin oxide (SnO) having 99.9% purity and a particle size of −500 mesh (classified from −325 mesh SO-601 powder, Atlantic Equipment Engineers, U.S.A) with an organic binder as used in Example 2 at 140° C. for 2 hours in a double-blade planetary mixer. The feedstock was granulated and injection-molded by using an injection molding machine having a clamping force of 80 ton to produce a tensile test specimen.

The tensile test specimen was placed in an alumina tray and then charged into a tube furnace. Debinding and sintering were performed in a single heating schedule while flowing an argon gas (a dew point of −53° C.) at a rate of 0.5 L/min as in Example 2, except that a sintering temperature and a sintering time were set to be 610° C. and 3 hours, respectively.

Sintered density of the sintered body of the tensile test specimen was determined to be about 97.9% compared to theoretical density via a density measuring method using the Archimedes principles. In a sintered condition, tensile strength was 204 MPa and elongation was 17.4%. After artificial aging (T6) at 170° C. for 8 hours following solution treatment at 540° C., the sintered body of the tensile test specimen showed tensile strength of 256 MPa and elongation of 2.3%.

Comparative Example 4

An injection molded body of a tensile test specimen containing 1 wt % SnO as used in Example 5 was debound and sintered in a single heating schedule as used in Example 5, except that a nitrogen gas of 99.99% high purity was used as an atmosphere gas and flowed at a rate of 0.4 L/min.

Sintered density of the sintered body of the tensile test specimen was determined to be about 97.9% compared to theoretical density via a density measuring method using the Archimedes principles. In a sintered condition, tensile strength was 235 MPa and elongation was 8.5%. After artificial aging (T6) at 170° C. for 8 hours following solution treatment at 540° C., the sintered body of the tensile test specimen showed tensile strength of 255 MPa and elongation of 0.4%.

Example 7

As in Example 4, Al-1 wt % Mg-0.5 wt % Si-0.25 wt % Cu blended powder containing air-atomized pure aluminum powder having an average particle size of 5 μm (MEP 105, Ecka Granules, Germany), magnesium powder having a −325 mesh size and 99.8% purity (Nana AMT, Korea), copper powder having a particle size of 1 to 5 μm and 99.% purity (CU-101, Atlantic Equipment Engineers, Inc., U.S.A), and silicon powder having a particle size of −10 μm, and 99.9% purity (SI-102, Atlantic Equipment Engineers, Inc., U.S.A), was mixed with 1 wt % of Sn having 99.9% purity (SN-101, Atlantic Equipment Engineers, U.S.A) and 5 wt % of silicon carbide powder by ball milling, and then was kneaded with an organic binder as used in Example 1 at 140° C. for 2 hours in a double-blade planetary mixer, thereby a 500 g of feedstock having a solids loading of 65% was prepared. The feedstock was crushed into granules and charged into an injection molding machine with clamping force of 80 ton to produce an injection molded body of an impeller (FIG. 7 (a)).

The injection molded body was charged into an Inconel retort installed in a box-type furnace, and debinding and sintering processes were performed as a single step under an argon gas atmosphere. An argon gas used at this time was dry with a dew point of −53° C., and flowed at a rate of 0.5 L/min. A temperature was increased from room temperature to about 100° C. in 1 hour and held for 1 hour; increased to 280° C. in 4 hours and held for 4 hours; increased to 380° C. for 4 hours and held for 4 hours; increased to 520° C. in 2 hours and held for 30 minutes; increased to 605° C. in 1.5 hours and held for 3 hours; and then allowed to cool.

A sintered body of a tensile test specimen produced as such exhibited a silver white color. The sintered body of the impeller manufactured as such is compared with the injection molded body in FIG. 7 (b).

Example 8

A feedstock having a solids loading of 67% was prepared by using composite powder containing AA6061 aluminum powder having an average particle size of 6 μm and 5 wt % of silicon carbide powder having an average particle size of 1 μm and 99.9% purity (SI 101, Atlantic Equipment Engineer, U.S.A), and an organic binder used in Example 3. An injection molded body of a small turbine was manufactured by using the feedstock and an injection molding machine with a clamping force of 80 ton. The injection molded body was charged into an Inconel retort inserted in a box-type furnace, and debinding and sintering were performed in a single heating schedule as in Example 7, except that a sintering temperature was changed to 610° C., a sintering time was set to 3 hours, and an argon gas was flowed at a rate of 0.3 L/min. FIG. 8 shows the appearance of a turbine sintered body manufactured as such.

Example 9

An end cap, i.e., a part of a miniature linear motion bearing, was manufactured by using a feedstock having a solids loading of 67% and containing AA6061 aluminum alloy powder as prepared in Example 3. Debinding and sintering were performed in a tube furnace in a single heating schedule under an argon atmosphere as in Example 3, and the sintering was performed at 610° C. for 2 hours. FIG. 9 (a) shows an injection molded body of an end cap manufactured as such, and FIG. 9 (b) shows appearance of a sintered body of the end cap. A dummy bar is temporarily added to a lower portion of a part having a “[” shape (FIG. 9 (c) so as to prevent distortion of a molded body, which may occur while debinding and sintering the injection molded body and the sintered body. The dummy bar is removed via machining after the sintering.

As described above, the present invention has been described with respect to the examples and drawings, but the present invention is not limited by this, and it is to be understood by one of ordinary skill in the art that various modifications and variations thereof may be possible without departing from the spirit and scope of the invention as set forth in the following claims. 

1. A powder molding method comprising: preparing a feedstock by kneading aluminum powder or aluminum alloy powder with a wax-based thermoplastic organic binder containing polyolefin copolymer having a carbonyl group; molding the feedstock to obtain a molded body; debinding the wax-based thermoplastic organic binder from the molded body to obtain a debound body; and sintering the debound body under an argon gas atmosphere for densification.
 2. The powder molding method of claim 1, wherein the wax-based thermoplastic organic binder contains 3 to 30 wt % of the polyolefin copolymer having the carbonyl group in total 100 wt %.
 3. The powder molding method of claim 1, wherein the polyolefin copolymer having the carbonyl group is maleic anhydride grafted polyethylene.
 4. The powder molding method of claim 1, wherein an average diameter of the aluminum powder or aluminum alloy powder is from 1 to 20 μm.
 5. The powder molding method of claim 1, wherein an aluminum alloy in the aluminum alloy powder is a commercial aluminum alloy composition containing at least 0.5 wt % of magnesium and selected from the group consisting of Al—Cu—Mg—(Mn) series (AA2xxx), Al—Mg series (AA5xxx), Al—Mg—Si—Cu series (AA6xxx), Al—Zn—Mg—(Cu) series (AA7xxx), or a composition containing 0.5 to 8 wt % of magnesium, 0 to 8 wt % of zinc, 0.1 to 3 wt % of copper, 0 to 5 wt % of silicon, 0 to 5 wt % nickel, 0 to 0.3 wt % of iron, 0 to 1 wt % of manganese, 0 to 0.5 wt % of zirconium, 0 to 0.5 wt % of chromium, 0 to 2 wt % of silver, 0 to 0.5 wt % of scandium, 0 to 2 wt % of lithium, and the balance of aluminum in total 100 wt %.
 6. The powder molding method of claim 1, wherein the aluminum alloy powder is a prealloyed powder produced by atomization of alloy in molten state, or blended powder in which pure aluminum and another alloying element powder or master alloy powder for addition of another alloying element are mixed.
 7. The powder molding method of claim 1, wherein the aluminum powder or aluminum alloy powder further contains 0.1 to 3 wt % of tin in total 100 wt %.
 8. The powder molding method of claim 1, wherein the aluminum powder or aluminum alloy powder further contains 0.3 to 5 wt % of tin oxide in total 100 wt %.
 9. The powder molding method of claim 1, wherein the molding is performed via powder injection molding, warm compression molding, or warm powder extrusion.
 10. The powder molding method of claim 1, wherein the debinding is performed under an atmosphere of an argon gas flowing at a rate of 0.1 to 20 L/min.
 11. The powder molding method of claim 1, wherein the debinding comprises partial debinding via solvent extraction or supercritical fluid extraction, and thermal debinding under an argon gas atmosphere.
 12. The powder molding method of claim 1, wherein the sintering is performed under at atmosphere of an argon gas flowing at a rate of 0.1 to 20 L/min.
 13. The powder molding method of claim 10, wherein the dew point of the argon gas is lower than or equal to −40° C.
 14. The powder molding method of claim 1, wherein the debinding and the sintering are performed in a single step in a same furnace under an argon gas atmosphere to remove the wax-based thermoplastic organic binder from the molded body and sinter the debound body.
 15. The powder molding method of claim 1, wherein a sintering temperature of the molded body using the aluminum powder as a raw material is between 630° C. to 655° C.
 16. The powder molding method of claim 1, wherein a sintering temperature of the molded body using aluminum alloy powder containing an alloying element of 0.5 to 12 wt % in total 100 wt % as a raw material is within a temperature range from a solidus temperature to a temperature where a liquid phase is formed within 30 vol. % in total 100 vol. %.
 17. The powder molding method of claim 1, wherein the aluminum powder or aluminum alloy powder further contains at least one reinforcing material selected from the group consisting of carbide selected from SiC, B₄C, TiC and WC, nitride selected from Si₃N₄, AlN, TiN, c-BN and h-BN, oxide selected from Al₂O₃, SiO₂, Y₂O₃, fly ash, and ZrO₂, sulfide including MoS₂, boride including TiB₂, hard cobalt alloy including T-800, powder, short fiber or whisker of a refractory metal such as W and Mo, polycarbon, graphite, carbon nanotube, graphene, and diamond.
 18. The powder molding method of claim 17, wherein an average diameter of the at least one reinforcing material is from 0.05 to 40 μm.
 19. The powder molding method of claim 17, wherein the at least one reinforcing material is contained in 0.1 to 30 wt % based on 100 wt % of the aluminum powder or aluminum alloy powder.
 20. A sintered body part produced by using aluminum powder, aluminum alloy powder, or aluminum-matrix composite material manufactured via the powder molding method of claim
 1. 21. The sintered body part of claim 20, being an impeller, a small turbine and a linear motion bearing end cap.
 22. (canceled)
 23. The powder molding method of claim 11, wherein the dew point of the argon gas is lower than or equal to −40° C.
 24. The powder molding method of claim 12, wherein the dew point of the argon gas is lower than or equal to −40° C. 